One minute your teenage daughter is having a relaxed, happy conversation with her friend on the phone.

The next, she stumbles over an algebra problem and is — instantly — as angry as you’ve seen her. She flings her pencil across the room, stomps up to her room, slams the door and shouts, “I hate my life!”

Your teenage son appears to be in a good mood, and you ask him in your best modulated tone if he remembered to empty the dishwasher. “Why are you always yelling at me? I hate this family!” he shouts, storming out of the room.

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For decades, parents have attributed such hair-trigger emotions to raging hormones, and they weren’t wrong. However, in recent years more has become known about how brain development — in concert with racing hormones — accounts for the differences in how teens act and think.

Psychologist David Walsh has written a book, “Why Do They Act That Way?” (Free Press), that offers an up-to-date explanation of the biological reasons for teens’ behavior and offers parents tips to communicate and stay connected with the kids.

Walsh, who is president and founder of the National Institute on Media and the Family, in Minneapolis, says parents often think kids are deliberately misinterpreting situations or trying to drive their parents crazy, but this isn’t the case.

It’s because a teenager’s prefrontal cortex — the brain’s center for moderation, impulse-control and the understanding of consequences — is still under construction. Simultaneously the body’s hormones — which Walsh calls the accelerator center of the brain — are surging.

“The prefrontal cortex is supposed to harness the accelerator center of the brain, but the impulse-control center is under construction,” said Walsh. “This is the reason teens are impulsive, risk-taking, quick to anger. The acceleration center of the brain is in high gear, while the brakes are on back order.”

Reading body language

In addition, Walsh said, the adolescent brain processes visual stimuli or body language differently than grown-ups do. In a study that asked adults and teens to interpret facial expressions, adults were more likely to correctly identify emotions, while adolescents often mistook fear or surprise for anger.

The study further showed, Walsh says, that adults rely on their prefrontal cortex to interpret facial expressions, while adolescents rely on the amygdala, in the anterior portion of the temporal lobe.

“Adults use the rational part of the brain to read emotions,” Walsh writes, “but adolescents basically do it with a gut reaction. And they are frequently wrong.”

Thus, a teenager may think a parent is yelling at them when they’re not, or they may think a peer is insulting them when that’s not the case.

Don’t ignore bad behavior

So, knowing all this, how can you better communicate with your child?

First of all, Walsh says that although it may not be the teen’s “fault” that he is volatile or erratic or impulsive, that does not absolve him or her of responsibility. Teens must learn to control their behavior, “and it’s your responsibility as a parent to help,” Walsh writes. “You can’t simply dismiss his behavior or let it go. … The experiences a teen has right now will have a big bearing on how he eventually learns to manage his own emotions and impulses.”

Walsh suggests sitting down with your teen in quiet times and discussing what behavior is expected and what the consequences will be if rules are not followed.

“Don’t communicate the consequences as threats,” Walsh writes. “Just let him know in a matter-of-fact way what will happen and that the consequences will be his own choices.”

Walsh emphasizes that parents should not get dragged into power struggles. “Teenagers are built for power struggles. The accelerator goes down to the floor so quickly,” he said.

But parents must keep their cool if their kid doesn’t.

When it’s time to enforce a consequence, Walsh says, do it calmly. Your child may want to argue, but don’t get drawn in.

“If you feel your blood pressure rising, take a deep breath and remember this advice: ‘When you feel like taking the wind out of his sails, it is a better idea to take your sails out of his wind.’ ”

In cases of extreme problems, Walsh suggests drawing up behavioral contracts that clearly spell out the rules and the consequences.

To reduce the level of misinterpretation between kids and grown-ups, Walsh suggests telling kids how you feel. He suggests prefacing statements with “I’m not angry, but it does irritate me when … ” or “Or I’m not angry, but I do worry when … ”